Heavy soles have been provided on golf clubs to lower their center of gravity and thereby improve the balance of the clubs during the stroke. For clubs that were made of wood (hence the term "woods" to refer to modern metal-only drivers), a heavy metal insert was precisely fitted onto the bottom of the wood piece. More specifically, to enable the wood to bear the load of the metal weight during the stroke, a precise fit between the metal weight and the wood piece of the head was required in two planes, one more or less vertical and one more or less horizontal.
The precise, small-tolerance fit between a lower, heavier piece of the club head and a lighter upper piece was retained when all-metal club heads were developed. For example, U.S. Pat. No. 5,527,034 to Ashcraft et al. discloses a golf club head having an aluminum or brass body and a separate sole that fits into cavity which must be machined into the body, with machining being necessary to fit the sole and body together, Ashcraft et al. abstract and col. 3, lines 62-63. While machining can be time consuming, it is easier to machine aluminum or brass club heads such as the Ashcraft et al. head than it is to machine heads made of titanium, tungsten, copper, and iron. Accordingly, as recognized herein a precise fit in two interface planes between a lighter upper head piece and a heavier lower head piece, particularly when one piece includes titanium, tungsten, copper, or iron, complicates manufacturing and increases the time and expense required for making the club head. Fortunately, the present invention recognizes that it is possible to provide a two-piece golf club head without requiring a multi-plane interface.